Conventionally, there has been known a multi-hop communication that is used in a communication network including a plurality of nodes. When information is transmitted between nodes, the multi-hop communication permits the relay of communication by at least one of the other nodes. As an aspect of the multi-hop communication, there has been also known a communication network in which one node as a master unit communicates to the other nodes as slave units instead of all nodes having equal relationship. For example, in order to perform remote meter reading, JP 2011-250301 A (hereinafter referred to as “document 1”) discloses a communication network that includes: a plurality of slave units (a plurality of slave stations) configured to respectively acquire meter reading results of consumers facilities; and a master unit (a master station) configured to collect the meter reading results from the plurality of slave units. In the technique described in document 1, when information of a meter reading result is transmitted to the master unit from any of the slave units, the relay by at least one of the other slave units is permitted, and the communication network that performs the multi-hop communication is constituted.
Incidentally, document 1 discloses that each slave unit is available both wireless communication and power line carrier communication, and forms a channel between the slave unit and the master unit by the wireless communication when failing to communicate by the power line carrier communication. That is, because the channel of the wireless communication is used as backup of the channel of the power line carrier communication, and it is not considered to properly distribute and use the channel of the power line carrier communication and the channel of the wireless communication.